The Drosophila laboratory is currently engaged in two major projects -- the genetic control of meiosis and the genetic organization of heterochromatin -- and three minor lines of investigation. With respect to meiosis, the approaches include: (1) an electron microscopical study of meiotic chromosomes in males carrying the disjunction-defective meiotic mutants, ord and mei-S332; (2) an examination of the influence of recombination-defective meiotic mutants on recombination in homozygotes for various X-chromosomal aberrations; (3) an analysis of a new meiotic mutant with a defect in the distributive segregational system. With respect to heterochromatin, we are continuing our analysis of the genetics and embryology of mutants in the da-abo region. The minor projects include a theoretical consideration of the maternal-age effect in Down's Syndrome in humans and on the process of mosaic fate-mapping in Drosophila, and a theoretical and experimental study demonstrating the existence of early-life components in the determination of the age of Death in Drosophila.